Also, there is a 4-term exact sequence [1]}:
\(\operatorname{Tor}_2^R(\operatorname{Tr}\Omega ^nM,N)\rightarrow \operatorname{Ext}^n_R(M,R)\otimes _RN\rightarrow \operatorname{Ext}^n_R(M,N)\rightarrow \operatorname{Tor}_1^R(\operatorname{Tr}\Omega ^nM,N)\rightarrow 0.\qquad \mathrm {(\ref {a1}.4)}\) 
